Sorry this video didn't turn out as well as I'd hoped but my external microphone developed a problem part-way through.
I took a look at this Futaba 9C to try and track down a fault that affected the aileron channel. Turns out that there was noise appearing on the signal line from the pot(entiometer) on the stick unit.
Often, noise like this indicates a dirty pot which can be replaced or cleaned -- however, not this time. When I disconnected the pot and substituted two fixed-value resistors instead, the noise was still there. This indicates that the circuit (the ADC) which converts the voltage from the stick into a binary value is likely to be faulty. In its "noisy" state, the ADC no longer passes changes in stick-voltage to the CPU so the aileron channel no longer functions or functions only slightly.
Since this was just a "quick look", I didn't take the logic board out or investigate further. If the owner wants, I will continue the diagnosis but that won't be for a week or so, due to other commitments.